Flower induction in June-bearing strawberry by intermittent low temperature storage

In this paper, we describe a new artificial flower-inducing treatment, intermittent low temperature storage, which we suggest could be a low-cost and useful technology for the forcing of June-bearing strawberries. Tray-grown 'Nyoho' plants were placed in a refrigerator (13°C, in the dark) for 4 days and then transferred to an outdoor shelter with 50% shading, also for 4 days (4D/4D). Plants were transferred at noon and this 4D/4D cycle was repeated twice. Similarly, 3D/3D and 2D/2D cycles were applied 3 and 4 times, respectively. The outdoor conditions during the period of treatment from late August to mid-September were as follows: mean daily temperature, 22.5 to 29°C; and day length (sunrise to sunset) 12.2 to 13.1 h. The efficient use of a refrigerator could be achieved by alternately subjecting two groups of plants to the same duration of low temperature in the dark and outdoor conditions. Treated plants were grown on peat bags and flowering performance was compared with untreated controls and continuously cold-stored (12D) plants. In intermittently cold-stored plants, flowering was significantly earlier than that in untreated controls by 6 to 10 days. Compared to the continuous 12D plants, flowering was 15 and 4 days earlier in 4D/4D plants within the plots planted on September 13 and 17, respectively. The 2 to 4 days under outdoor conditions imposed in the low temperature storage apparently induced uniform flower initiation through the improvement of carbohydrate nutrition in strawberries. Although further studies are required to establish the most effective treatment procedures, intermittent low temperature storage could be a useful new flower-inducing technology for early forcing of June-bearing strawberries.